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DIGISONDE-4D
SYSTEM MANUAL
VERSION 1.2.11
2-6 SECTION 2 - INSTALLATION, SETTING UP AND FIELD VALIDATION
Distance Constraints
2:21. The following spatial distance constraints in the system layout must be adhered to in order to ensure
optimum operation:
a. Standard RG-213 cable length from any receive antenna to the sounder is 150 m. Depending on
the local RF environment up to 300 m lengths of RG-213 can be used. If the distance to the
sounder from any receive antenna is to be greater than 300 m then consult with LDI.
b. The distances between the three antennas at the corners of the equilateral triangle should be the
same to within 1 meter. Similarly, the distances from the center antenna to the three corners of the
triangle should be the same within 1 meter.
c. If there are difficulties with the receive antenna layout, it is allowable to reduce the size of the tri-
angle from 60 meters to 45 meters. If space permits, the default receive antenna array orientation
is to have one leg of the triangle running North - South Geographically, but this is not critical and
secondary to some other considerations. In any case, it will be necessary to know the relative po-
sitions of the four receive antennas with 1/2 meter accuracy for the DPS4D configuration files.
d. If there is any question about the proper positioning of the Receive Loop antennas, particularly in
regard to proximity to obstructions and the transmit antenna, it might be best to install them tem-
porarily, just sitting on top of the ground, and pour concrete only after LDI has evaluated the per-
formance of the antennas.
Transmit Antenna
2:22. The crossed delta transmit antenna has been designed using the NEC modeling program. The design
objectives were for a simple antenna that optimally transmits circularly polarized waves vertically upward
for frequencies between 2 and 16 MHz. LDI usually has this transmit antenna built by a major antenna
manufacturer. The Digisonde
®
user may build his own transmit antenna in consultation with LDI. The tower
is 30.5 meters (100 ft.) high. It will require a square ground area 44 meters x 44 meters (144 ft. x 144 ft.) for
installation. In addition there are recommendations for spacing from the receive antennas.
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